In the last article of this series I discussed artificial sweeteners, and gave you my take on whether you should include them in your diet. This week, I want to talk about sugar alcohols, which are another popular low-calorie sugar substitute.

Xylitol is the most popular and most extensively researched, so I’ll focus my discussion on it, but the general takeaway of this article applies to other sugar alcohols as well, such as sorbitol and erythritol.

Xylitol and sorbitol are commonly used as sugar replacements, but are they safe? Here’s what you need to know!

What exactly are sugar alcohols?

Sugar alcohols are a type of ‘low-digestible carbohydrate,’ a category that also includes fiber and resistant starch. Sugar alcohols occur naturally in many fruits and are also known as ‘polyols,’ which you may recognize as a FODMAP. Unlike artificial sweeteners, sugar alcohols aren’t completely calorie-free, because we are able to digest and absorb them to some extent. The absorption rate varies among sugar alcohols, from about 50% for xylitol to almost 80% for sorbitol, depending on the individual. Erythritol is almost completely absorbed, but is not digested, so it provides almost no calories.

Compared with artificial sweeteners, sugar alcohols have very few safety and toxicity studies, and are generally accepted as safe. In one long-term human study, 35 participants consumed xylitol as their primary dietary sweetener for two years, and no adverse effects other than GI distress were observed, and GI symptoms dissipated after the first couple months. The amount of xylitol consumed during this trial regularly exceeded 100g per day, often going over 200g per day, depending on the participant.

Metabolic effects of sugar alcohols

Sugar alcohols are a popular choice for weight loss due to their reduced calorie content, and for diabetics due to their low glycemic index. There’s not nearly as much research on the metabolic effects of sugar alcohols as there is on artificial sweeteners, but the evidence we have suggests that sugar alcohols are at least harmless, and possibly beneficial.

For the most part, sugar alcohols cause no appreciable changes in blood glucose or insulin in humans, and sorbitol and xylitol have not been found to raise blood glucose following consumption. In diabetic rats, 5 weeks of xylitol supplementation (as 10% of their drinking water) reduced body weight, blood glucose, and serum lipids, and increased glucose tolerance compared with controls. Two other rat studies also found that xylitol-supplemented rats gained less weight and fat mass compared with control rats, and had improved glucose tolerance.

Because sweetness does not predict caloric value in sugar alcohols, one might expect that they would cause the same ‘metabolic confusion’ that is seen with noncaloric artificial sweeteners. Unfortunately there isn’t enough evidence to form a conclusion about this, but my feeling based on what I’ve read is that this isn’t a significant issue for sugar alcohols.

For one, sugar alcohols aren’t ‘intense sweeteners’ like artificial sweeteners, which are hundreds of times sweeter than sugar. In fact, many are less sweet than sugar. Also, sugar alcohols do provide some calories, so there’s not as much of a discrepancy between the caloric load your body expects and the caloric load it actually gets.

Does xylitol prevent tooth decay?

The most well-known health benefit of xylitol is easily its effect on dental health, and evidence for xylitol’s ability to prevent tooth decay is pretty robust. A couple trials have found xylitol to be more effective at preventing cavities than fluoride, and benefits of xylitol consumption have even been observed in children whose mothers chewed xylitol-containing gum. Unsurprisingly, the most drastic effects are observed when xylitol replaces sucrose in either the diet or in chewing gum, but significant reductions in cavities have been observed when xylitol is simply added on top of a normal diet as well.

Although some effects of xylitol are undoubtedly due to nonspecific factors such as increased saliva production or the replacement of sugar, it does appear to have specific properties that support dental health. Xylitol is not fermentable by common plaque-forming oral bacteria like sugar is, so it doesn’t provide a food source. Additionally, xylitol actively inhibits the growth of these bacteria. It also forms complexes with calcium, which may aid in remineralization.

Sugar alcohols and digestive health

While sugar alcohols appear to be safe and potentially therapeutic, they are also notorious for causing digestive distress. Because sugar alcohols are FODMAPs and are largely indigestible, they can cause diarrhea by pulling excess water into the large intestine. The fermentation of sugar alcohols by gut bacteria can also cause gas and bloating, and sugar alcohols may decrease fat absorption from other foods. However, most evidence indicates that people can adapt to regular sugar alcohol consumption, and the adverse GI effects reported in studies tend to fade after the first month or two.

Erythritol is probably the best-tolerated sugar alcohol, and a few human trials have found that if the amount of erythritol is gradually increased and doses are spread throughout the day, many people can tolerate large amounts (up to1g/kg of body weight) of erythritol without GI distress. The average tolerance for xylitol and sorbitol is lower; most study subjects could tolerate about 30g per day without a problem, but significant adaptation was necessary to increase xylitol content in the diet.

A few studies indicate that sugar alcohols may have a prebiotic effect. This isn’t too surprising, considering the prebiotic effects of other low-digestible carbohydrates such as fiber and resistant starch. Animal studies have found that xylitol causes a shift from gram-negative to gram-positive bacteria, with fewer Bacteroides and increased levels of Bifidobacteria. A similar shift has been observed in humans, even after a single dose of xylitol. Additionally, the shifts observed allowed for more efficient use of the sugar alcohols by gut bacteria, which largely explains the reduction in GI symptoms after a few months of regular consumption.

In addition to the potential metabolic, dental, and prebiotic benefits already discussed, xylitol shows promise for preventing age-related decline in bone and skin health. One interesting study found that 10% xylitol supplementation over 20 months increased collagen synthesis in the skin of aged rats, resulting in thicker skin. Preliminary rat studies have also shown that xylitol can increase bone volume and mineral content and protect against bone loss.

Overall, sugar alcohols appear to be safer than artificial sweeteners with several potentially therapeutic effects. Although the metabolic and weight loss benefits of sugar alcohols haven’t been studied as extensively, I would recommend sugar alcohols over artificial sweeteners to anyone who needs a low-calorie sweetener, although I wouldn’t recommend that anyone consume huge amounts of them. I’ll also be interested to see additional research on their ability to alter the gut microbiome and disrupt biofilms, because this could make sugar alcohols a useful tool for certain patients.

At this point, there don’t seem to be any major problems with sugar alcohols, so if it’s something you’re interested in, I would experiment with your own tolerance and see how they affect you. However, people with gut issues should be cautious.

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